1. Field of the Invention
The present invention relates to a motor-driven camera and, more particularly, to a motor-driven single-reflex camera of the type which utilizes a motor to carry out various photographic operations such as the operation of moving up and down a movable mirror and the operation of effecting shutter charging operation.
2. Related Background Art
In a single reflex camera of the TTL metering type in which its photometric system for automatic exposure adjustment (hereinafter referred to the "AE") and automatic focus adjustment (hereinafter referred to as the "AF") is arranged to receive light flux passed through a photographing lens and reflected from a movable mirror, in order to achieve accurate photometry, it is necessary to start photometry after mirror bounds due to the shock occurring when the movable mirror has descended calm down and the movable mirror has come to a rest accurately at a predetermined down position. In particular, in the case of continuous shooting, the above necessity is an essential consideration.
Accordingly, a conventional method of starting photometry utilizes a switching means which can be switched between the ON and OFF states when the movable mirror has moved to its down position. In this method, after it has been determined, through the switching means, that the movable mirror has completed its mirror-down operation, photometry is started after a predetermined estimated time period has passed which corresponds to the time period required for the mirror bounds to disappear. A simplified method has also been proposed in which, after the reception of the detection signal of a detecting means for detecting whether or not shutter running has been completed, photometry is started after a predetermined time period including a mirror-down period.
However, in the case of the former method of starting photometry when the predetermined time period has passed after the detection of the completion of the mirror-down operation, the switching means need to be added to a mirror driving mechanism in order to detect the time of the completion of the mirror-down operation. Accordingly, it has been impossible to avoid the problem that the mirror driving mechanism inevitably becomes complicated.
In the case of the latter method of starting photometry when the predetermined time period has passed after the detection of the completion of the shutter running operation, the following problems are encountered. More specifically, a conventional motor-driven type of cameras which are capable of film winding and shutter charging is arranged such that a movable mirror is moved up and down by the urging force of a spring which is charged during film winding. Accordingly, there is no risk that the time period required for the mirror-down operation is changed due to variations in the level of source voltage. However, many of built-in motor cameras which have recently been developed are arranged such that a movable mirror is also driven directly by a motor to move up and down. In such a case, the length of the time period required for the mirror-down operation varies in accordance with variations in the level of the source voltage.
Accordingly, in the latter method, in order that the wait time required from the completion of shutter running to the starting of photometry can be made constant even if the level of voltage supplied to the motor varies, the wait time is selected to be somewhat long so as to cope with a case where the level of the source voltage falls. Accordingly, although the mirror-down operation is completed in a short time when the level of the source voltage is high, it has been impossible to increase the film tranporting speed for continuous shooting since photometry cannot be started at an earlier time because of the presence of such wait time.